The use of open coil heaters, either as single stage or multistage arrangements, is well known in the industry. Generally, these heaters comprise one or more resistance wire heating coils, insulators to electrically isolate and support the coils on a plate or frame, ductwork to create a flow channel for forced air to flow over the coils for heating, and a termination assembly wherein the ends of the coil are linked to a source of power.
One example of this art is demonstrated in U.S. Pat. No. 4,268,742 to Cottrell et al. and U.S. Pat. No. 5,329,098 to Howard et al., herein incorporated in their entirety by reference. Other examples are demonstrated by product literature published by TUTCO, Inc. of Cookeville, Tenn.
One significant aspect of open coil heater art is that of mounting heaters into metal ducts. The prior art for heaters mounted into heater ducts is limited to single position mounting of the termination and heater support ceramics. This is because rotating the heater 180° about the axis of the heater duct will change the relationship of one or more of the heater coils, the support ceramics or the heater termination so that a temperature sensing devices will not operate properly in the rotated position. Another feature is that in some designs the heater orientation can only be in one position because movement of the heater coil due to gravity during heating has been accounted for in one direction only.
Another prior concept of mounting heaters into ductwork is that of attaching the heater structure in such a manner as to ensure the heater is affixed to the ductwork. In the prior art either fasteners, tabs, tensioning spring clips or some combination of these are used. Fasteners and tensioning spring clips are well known and an example of a tab mounting technique that requires no fasteners can be found in U.S. Pat. No. 5,895,597 to Sherrill, also incorporated by reference herein in its entirety. The tab mounting shown in this patent permits expansion and contraction of the mounting plate due to thermal cycling. It should be also noted that the heater support plate and termination assembly in this heater are mounted in only one of the duct halves. This arrangement precludes the heater's use in another installation due to the location of the terminal block on the one duct half.
In the prior art for multi-stage heaters, electric coil ends reaching from the heated sections to the element terminals must span distances that expose the wires to potential grounding or contact with electrically live parts. Such exposure requires electrical isolation of these transition sections. Isolation is accomplished by ceramic tubes as disclosed in U.S. Pat. No. 5,925,273 to Sherrill or by special standoff insulators defined in U.S. application Ser. No. 10/879,286 to Howard et al., each owned by the present assignee, Tutco, Inc.
In the prior art for single stage heaters, the use of a coil configuration to position the single open coil element on both sides of a metal mounting plate can be found in the above-referenced U.S. Pat. No. 4,268,742. This art demonstrates a FIG. 8 coil path configuration.
One common application for single or multistage open coil resistance wire heaters is for installation as part of other heating equipment or appliances, e.g., clothes dryers. The manufacturer of appliances and equipment, especially a clothes dryer manufacturer, often requires multi-stage open coil electric heaters mounted in a heater duct. Prior art multi-stage heaters are designed to be operated in a given position within the duct. Termination components, wherein the resistance wire coils straighten to form lead wires for connection to a terminal assembly, heater support insulators or ceramics, and over temperature limit controls are set in precise locations in these types of equipment.
In certain applications, appliances are needed that are commonly called left-hand and right-hand mounting. That is, certain heater components like the termination assembly, limit controls and the like may be located on one side of the heater in one installation, and required to be located on the other side of the heater in another installation. When an appliance is designed with a multi-stage open coil electric heater mounted in a duct, maintaining the left hand-right hand heater and heater duct relationship requires two heater designs. This is because in the prior art, heaters are designed only for one orientation whereby one heating assembly is used for a right hand connection and another heating assembly would have to be used for the left hand assembly.
Because of this two heater design requirement, a burden is imposed on the appliance maker and heater manufacture, thereby increasing the costs for both parties. As such, there is a need in the industry for a heater design concept that will permit a single heater to be used in left-hand or right-hand heater duct orientations. The present invention satisfies this need by providing a single heater assembly design equally adapted for left and right hand installations.